At this point Operations Dashboard doesn't have the capability to expand custom widgets. However, this is one of the features we want to implement as this requirement is already requested by a few customers (including you). Ideally, it will be a property that you can configured in the manifest.
Meanwhile, could you tell me a bit more about what kind of custom widget you're building that you want it to be expandable, and how will the "enlarged view" bring benefits to the users of your widget? It will be best if you could share some screenshots, prototypes or even a sample. Any other information you want us to know will be appreciated too.